Abstract
The poor physical property and strong heterogeneity of Triassic Yanchang formation in Huanjiang oilfield of Ordos Basin are the main reasons for uneven water absorption, partial injection wells underinjection at high pressure, and decline of production. Previously, large numbers of conventional acidifications were used for plugging removal in the reservoir, but the effect was not so good and effective period was short. Aiming at the geological characteristics of Huanjiang oilfield, an online shunt acidification and augmented injection technology which does not stop water injection, pull original production strings out, and continuously inject acid and diverting agent has been proposed. A chelating acid COA-1S with low corrosion rate (0.3675 g/(m2·h)), good retardation capacity (hydrolysis constant = 1.2 × 10−6), and effective chelating ability (precipitation inhibition rate >95%) has been developed, as well as a diverting agent COA-1P with good dispersion in acid solution, diversion effect, and particle size (10–100 μm), which behaves well in COA-1S acid. It has been proved that the online acid system has a good diversion acidizing ability and plugging removal performance in a deep area in the laboratory core physical simulation test. The field test results show that the online shunt acidizing and augmented injection technology could reduce the injection pressure significantly (4.2 MPa) and increase water injection by 10 m3/d for the measured well (H5) and improve the water injection profile prominently. The online shunting acidification and augmented injection technology have the following advantages: simple procedures, fewer equipment needed, high efficiency of depressurization, and increasing water injection, which could effectively improve the profile of water wells, and there is a bright future of the technology.
Highlights
Introduction e main development layer of Huanjiang oilfield is the Triassic Yanchang formation, the average porosity of the reservoir is 10.9%, and the average permeability is 0.43 × 10−3 μm2, so Huanjiang oilfield belongs to the ultra-low-permeability sandstone reservoir
Based on the geological characteristics of Huanjiang oilfield, an online shunt acidification and augmented injection technology with not stopping water injection, not pulling out the original production strings, and continuous injection of acid have been proposed. e field test results showed that the technology behaves well, which could greatly reduce the water injection, improve the water injection volume, and effectively improve the profile of the wells
In order to further verify the feasibility of the technology, parallel core flow tests are carried out using two cores with different permeabilities selected from the corresponding reservoirs in Huanjiang oilfield [10, 11], and the effects of shunt and acidification are analyzed. e experiment temperature is 60°C, and the experiment apparatus is the multifunctional shunt acidification experiment instrument which is self-developed. e results are shown in Figure 3 and Table 3
Summary
K- permeability, 10−3 μm; ΔP- pressure difference, MPa; μ- injection viscosity, mPa·s; L- distance of pressure differential, m3; and N- total amount of layers. It can be seen that the solution is clear and transparent when diverting agent COA-1P mixes with tap water, and when mixing diverting agent COA-1P with the chelate acid COA-1S, uniform and dispersed white small particles are produced. Erefore, the size of the particle could be changed by adjusting the concentration of the acid liquid and the diverting agent, so as to achieve the purpose of blocking the high-permeability layer temporarily and meet the shunting requirements [8, 9]. E compatibility tests for the chelate acid COA-1S and diverting agent COA-1P with injected water and formation water are carried out under the conditions of 20 and 60°C, respectively. Compatibility Evaluation. e compatibility tests for the chelate acid COA-1S and diverting agent COA-1P with injected water and formation water are carried out under the conditions of 20 and 60°C, respectively. e results show that the compatibility of the two liquids with injected water and the formation water is good at different temperatures
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